Biometric authentication systems are used for authenticating users. Biometric sensing technology provides a reliable, non-intrusive way to verify individual identity for authentication purposes.
Fingerprints, like various other biometric characteristics, are based on unalterable personal characteristics and thus are a reliable mechanism to identify individuals. There are many potential applications for utilization of biometric and fingerprints sensors. For example, electronic fingerprint sensors may be used to provide access control in stationary applications, such as security checkpoints. Electronic fingerprint sensors may also be used to provide access control in portable applications, such as portable computers, personal data assistants (PDAs), cell phones, gaming devices, navigation devices, information appliances, data storage devices, and the like. Accordingly, some applications, particularly portable applications, may require electronic fingerprint sensing systems that are compact, highly reliable, and inexpensive.
Various electronic fingerprint sensing methods, techniques, and devices have been proposed and/or are currently in use or under development. For example, optical and capacitive fingerprint sensing devices are currently on the market. Like a digital camera, optical technology utilizes visible light to capture a digital image. In particular, optical technology may use a light source to illuminate an individual's finger while a sensor, e.g., a charge-coupled device (“CCD”) captures an analog image. This analog image may then be converted to a digital image. Other sensors may be pressure based, e.g., using piezoelectric materials or deformable capacitive sensors, impedance based, such as resistive sensors, heat based, etc.
There are generally two types of capacitive fingerprint sensing technologies: passive and active. Both types of capacitive technologies can utilize similar principles of capacitance changes to generate fingerprint images. Passive capacitive technology typically utilizes a linear one-dimensional (1D) or a two-dimensional (2D) array of plates (i.e., electrodes or traces) to apply an electrical signal, e.g., in the form of an electrical field, such as a varying high speed (radio frequency (“RF”) or the like) signal transmitted to the finger of the user from a transmitter trace and received at a receiver trace after passage through the finger. A variation in the signal caused by the impedance of the finger indicates, e.g., whether there is a fingerprint valley or ridge between the transmitter trace and the receiver trace in the vicinity of where the transmission and reception between the traces occurs. Fingerprint ridges, as an example, can typically display far less impedance (lower capacitance across the gap) than valleys, which may exhibit relatively high impedance (higher capacitance across the gap). The gaps can be between traces on the same plane, horizontal, or in different planes, vertical.
Active capacitive technology is similar to passive technology, but may require initial excitation of the epidermal skin layer of the finger by applying a current or a voltage directly to the finger. Typically, thereafter, the actual change in capacitance between the source of the voltage or current on an excitation electrode (trace) and another receptor electrode (trace) is measured to determine the presence of a valley or ridge intermediate the source electrode and the another receptor electrode. Active capacitive sensors, however, may be adversely affected by such effects as dry or worn finger print components. By contrast, passive sensors are typically capable of producing images regardless of contact resistance and require significantly less power, e.g., because of more penetration of the layer of skin of the user in the vicinity of the transmitter/receiver pair.
In some embodiments the traces may form a plurality of transmitter electrodes and a single receiver electrode or a plurality of receiver electrodes and a single transmitter electrode arranged in a linear one dimensional capacitive gap array. In such embodiments the capacitive gape may be horizontal across the gap formed by the respective ends of the plurality of traces and the single trace, whether transmitter or receiver. Advantageously such sensor systems can be very compact, inexpensive to manufacture, with the sensor element traces simply formed on a substrate, such as a flexible substrate, made of, e.g., Kapton® tape made by 3M, and reliable, e.g., due to insulation of the finger of the user from the traces and/or electric contact, etc.
In some embodiments, the traces may form a 2D grid array, e.g., with rows of transmitter/receiver traces on one substrate and columns of receiver/transmitter traces on the same or a separate substrate, e.g., laminated together with some form of dielectric between the traces to form a 2D sensor element array. Such 2D arrays may be essentially as long as the last digit of the finger forming a placement sensor element array, or shorter in the direction of the length of the finger, forming a swiped 2D array. While both the 1D linear array sensors systems and the 2D array sensor systems can operate in essentially the same way, i.e., with transmission of a signal from a transmitter trace to a receiver trace, the 2D arrays are larger in the region that must be exposed in the vicinity of the finger being sensed, and are generally more complex electronically. In addition such 2D arrays can involve higher degrees of noise and other impediments to accurate signal processing of the received signals and also more complicated software and hardware for reconstructing the fingerprint from a series of swiped 2D images accumulated during sensing in the direction of the finger and sensor elements relative movement during the swipe.
Although each of the fingerprint sensing technologies described above may generate satisfactory fingerprint images, each may be adversely affected by noise, interference, and other effects. For example, capacitive sensors may be particularly susceptible to noise and parasitic capacitive coupling, which may degrade the quality of the acquired fingerprint image. 2D arrays may be more so susceptible than linear 1D arrays. Prior attempts to reduce noise in 2D sensors have employed reference capacitors positioned at each sensor pixel to provide a method of subtracting noise contributions that affect both the finger capacitance and the reference capacitor. This technique is most effective for electrical noise at the pixel level, as seen, e.g., in U.S. Pat. No. 8,115,497B2, PIXEL SENSING CIRCUIT WITH COMMON MODE CANCELLATION, issued on Feb. 14, 2012, to Gozzini, and/or US Pub. No. US 2012/0085822 A1, entitled FINGER SENSING DEVICE INCLUDING DIFFERENTIAL MEASUREMENT CIRCUITRY AND RELATED METHODS, published on Apr. 12, 2012, referenced above. Also proposed has been the user of a reference electrode external to the sensor array, e.g., that is not affected by an actual presence of the finger of a user, such as is discussed in U.S. Pat. No. 8,421,890 B2, entitled ELECTRONIC IMAGER USING AN IMPEDANCE SENSOR GRID ARRAY AND METHOD OF MAKING, issued to Benkley on Apr. 16, 2013. Accordingly, it would be an advance in the art to reduce the effects of noise, parasitic capacitive coupling, and other effects in capacitive-type fingerprint sensing circuits.
Two-dimensional matrix format fingerprint readers have historically been built with row and column multiplexing circuits along the edge of the sensor pixel array, e.g., as illustrated in U.S. Pat. No. 7,616,786 B2, entitled FINGER BIOMETRIC SENSOR WITH SENSOR ELECTRONICS DISTRIBUTED OVER THIN FILM AND MONOCRYSTALLINE SUBSTRATES AND RELATED METHODS, issued to Setlak, et al., on Nov. 10, 2009; U.S. Pat. No. 7,835,553 B2, entitled IDENTITY AUTHENTICATION DEVICE AND FINGERPRINT SENSOR, issued to Miyasaka on Nov. 16, 2010 and U.S. Pat. No. 7,755,369 B2, issued to Chuang, et al. Mar. 23, 2010, entitled CAPACITIVE FINGERPRINT SENSOR AND THE PANEL THEREOF. This is true of both silicon substrate and glass substrate fingerprint readers. The use of such row and column multiplexing circuits all the signals to and from the individual rows and columns to be carried over a small number of signal lines. This has been done within a controller IC, but this makes the controller IC more expensive both from the standpoint of circuitry included in the IC and thus chip real estate utilized, as well as input/output connections required in the chip packaging.
According to co-pending U.S. Patent Pub US 2013/0177220 A1, entitled METHODS AND DEVICES FOR CAPACITIVE IMAGE SENSING, published Jul. 11, 2013, noise reduction in a 1D sensor array can be accomplished by subtracting an NI (background) signal from the primary finger influenced (“FI”) signal as a means of subtracting out noise signals, e.g., that affect adjacent receiver lines in a linear sensor.
The emergence of portable electronic computing platforms allows functions and services to be enjoyed wherever necessary. Palmtop computers, personal digital assistants (“PDAs”), mobile telephones, portable game consoles, biometric/health monitors, and digital cameras are some everyday examples of portable electronic computing platforms. The desire for portability has driven these computing platforms to become smaller. Such portable electronic computing platforms, as well as some larger ones like lap top computer, pads and pods, electronic tablets and the like have been increasingly shown to be in need of authentication of the user to access the device or once on the device to access applications running on the device and/or to access remote applications such as websites, web-pages, user accounts, such as email of social network accounts, and engage in various forms of on-line transactions, each requiring varying degrees of authentication of the user to the device/application and the application to the user. Such processes have increasingly required input from the user of user information, e.g., in the form of user name and password/PIN, but even more so more sophisticated and secure forms of user authentication to the relying party and vice versa. For this purpose various forms of biometric user identification input, e.g., fingerprint authentication information is being required.
It is difficult to efficiently collect user authentication input information, e.g., fingerprint images or fingerprint authentication determinations and the like on these ever-smaller personal computing and communication devices. In addition, such as portable electronic computing platforms need other forms of user inputs for multiple purposes including, but not limited to, navigation: moving a cursor or a pointer to a certain location on a display; selection: choosing, or not choosing, an item or an action; and orientation: changing direction with or without visual feedback. Where the usual form of a GUI input device, e.g., an actual or virtual mouse may easily be used with and transported with a lap top computer or larger touch screen device, such as a tablet, smaller devices with concomitantly smaller display areas, such as cell phones, pads and pods, Blackberrys, etc. can be perfect candidates for sensors, such as biometric sensors and/or buttons and/or combinations thereof that can perform authentication as well as act as GUI input devices.
Prior art systems have borrowed concepts for user input from much larger personal computers. Micro joysticks, navigation bars, scroll wheels, touch pads, steering wheels and buttons have all been adopted, with limited success, in today's portable electronic computing platforms. All of these devices consume substantial amounts of valuable surface real estate on a portable device. Mechanical devices such as joysticks, navigation bars and scroll wheels can wear out and become unreliable. Because they are generally physically designed for a single task, they typically do not provide functions of other navigation devices. Their sizes and required movement on or within the device often precludes optimal ergonomic placement on portable computing platforms. Moreover, these smaller versions of their popular personal computer counterparts usually do not offer accurate or high-resolution position information, since the movement information they sense is too coarsely grained.
Most commercially available biometric image sensors, such as fingerprint image sensors that detect and measure features (e.g., valleys, ridges, and minutiae) on the surface of a finger using capacitive, thermal, optical, or other sensing technologies as noted above, fall into the two above noted categories: (1) full-size placement sensors and (2) typically smaller so-called swipe sensors, with the latter being either 1D or 2D. Placement sensors have an active sensing surface that is large enough to accommodate most of the interesting part of a finger at the same time. Generally, they are rectangular in shape with a sensing surface area of at least 100 mm2. The finger is held stationary while being imaged on the full-placement sensor.
The other type of finger image sensor, called a swipe sensor, is characterized by a strip-like imaging area that is fully sized in one direction (typically in length) but abbreviated in the other (typically width). An example is the Atrua Wings ATW100 sensor, as described by Andrade in US Patent Application US 2003/0016849 A1 published Jan. 23, 2003 (issued as U.S. Pat. No. 7,256,589 B2 on Aug. 14, 2007), and PCT publication WO 02/095349. A finger is swiped across the sensor until all parts of it are imaged, analogous to how a feed through paper document scanner operates. A sequence of slices or frames of the finger image is captured and processed to construct a composite image of the finger. As shown in U.S. Pat. No. 7,099,496 B2, entitled SWIPED APERTURE CAPACITIVE FINGERPRINT SENSING SYSTEMS AND METHODS, issued to Benkley on Aug. 29, 2006 shows a limiting case where the sensed “area” is a single linear 1D array of capacitive gaps.
Several prior art devices use a touchpad for authenticating a user and moving a cursor on a display device. A touchpad, which operates similarly to a finger image sensor, does not provide enough image resolution or capability to distinguish ridges and valleys on the fingerprint. Instead, the touchpad perceives a finger as a blob and tracks the blob location to determine movement. Therefore, a touchpad cannot follow miniscule movements, nor can it very easily detect rotational movement.
U.S. Patent Publication No. US 2002/0054695 A1, titled “Configurable Multi-Function Touchpad Device,” to Bjorn et al. discloses a touchpad that can be configured to authenticate a user or to control a cursor. The touchpad attempts to enhance the function of a touchpad to include fingerprint capability. It merely absorbs the hardware of a capacitive finger image sensor into the much-larger size touchpad to achieve cost-savings. It does not disclose using the finger image data of the data collector for navigation or other device control. Moreover, as conceived, the apparatus of Bjorn, with its large size will preclude the touchpad from being used in most portable electronic computing platforms.
U.S. Pat. No. 6,408,087 B1, entitled CAPACITIVE SEMICONDUCTOR USER INPUT DEVICE, issued to Kramer on Jun. 18, 2002 discloses a system that uses a fingerprint sensor to control a cursor on the display screen of a computer. The system controls the position of a pointer on a display according to detected motion of the ridges and pores of the fingerprint. The system has a number of limitations. It uses image-based correlation algorithms and, unlike a system using a swipe sensor, requires fingerprint images with multiple ridges, typical for capacitive placement sensors. To detect a motion parallel to the direction of a ridge, the system requires the sensor to detect pores, a requirement restricting its use to high-resolution sensors of at least 500 dpi. The system detects changes in ridge width to sense changes of finger pressure. However, ridge width measurement requires a very high-resolution sensor to provide low-resolution of changes of finger pressure. The algorithm is unique to emulating a mouse and is not suitable for emulating other types of input devices, such as a joystick or a steering wheel, where screen movements are not always proportional to finger movements. For example, a joystick requires a returning to home position when there is no input and a steering wheel requires rotational movement. The system is unique to capacitive sensors where inverted amplifiers are associated with every sensor cell.
Capacitive fingerprint sensor arrays are often required to sense very small signals (e.g. associated with passive modification of a transmitted signal due to femtofarad differences in capacitance, e.g., between a transmitter electrode (trace) and a receiver electrode (trace) due to the difference between the electric field passing from the transmitter to the receiver through a finger of a user passing through a ridge or a valley of the fingerprint of the user. This can be especially so when attempting to read a fingerprint through a somewhat thick cover layer (0.100 mm or more, for example) of glass or other dielectric material. In one-dimensional fingerprint sensors which use a linear array of transmitters and a single receiver electrode, it has been suggested that the signal strength on the receiver line can be boosted by activating multiple transmitters simultaneously transmitting to the single receiver or multiple receivers receiving from the single transmitter trace, e.g., as discussed in co-pending US Patent Pub. US 2013/0177220 A1, entitled METHODS AND DEVICES FOR CAPACITIVE IMAGE SENSING, published Jul. 11, 2013.
Noise reduction methods have been proposed for 2D sensor arrays as well, as exemplified in U.S. Patent Pub. US 2013/0265137 A1 published Oct. 10, 2013, entitled INTEGRATABLE FINGERPRINT SENSOR PACKAGINGS.
A similar problem(s) can exist for two-dimensional fingerprint sensors as has been suggested for resolution in 1D linear sensor arrays, and the problem may be further complicated by the additional parasitic capacitances resulting from row/column crossovers that are not present in a one-dimensional (linear) sensor array. In order to alleviate this problem, the vast majority of capacitive two-dimensional fingerprint sensors therefore incorporate not only the capacitive sensing electrodes in each sensor pixel, but also amplification circuitry to boost the signal before it travels down the row or column line to a multiplexer or other readout circuit. The signal produced by the presence or absence of a fingerprint ridge can be further boosted by combining the signals from several receiver pixels adjacent to, or surrounding, a primary transmitter pixel, as is discussed, e.g., in US Pub US 2012/0085822 A1, with named inventors Setlak et al., published on Apr. 12, 2012.
Fingerprint readers that are intended to be at least to a large degree transparent are often fabricated on transparent glass. In this case the row and column drive and readout circuits may be contained in a silicon IC that is attached to, i.e., mounted on, the glass. However, the large number of rows and columns and fine pitch of these lines, especially on the silicon IC, requires very high resolution die attach processes and connector pads, or it may also make the silicon IC larger than necessary, to fit all the input & output pads that are necessary. For this reason fingerprint readers built on glass substrates have been built all the necessary row/column multiplexing circuits (often as well as sense amp circuits) in thin film transistor (“TFT”) circuits fabricated directly on the glass, as shown, e.g., in U.S. Pat. No. 7,616,786 B2, entitled FINGER BIOMETRIC SENSOR WITH SENSOR ELECTRONICS DISTRIBUTED OVER THIN FILM AND MONOCRYSTALLINE SUBSTRATES AND RELATED METHODS, issued to Setlak on Nov. 10, 2009, where the circuitry for an operation amplifier is split between lower cost TFTs at the sensor array location and higher performance transistors within a remotely mounted control IC; U.S. Pat. No. 7,835,553 B2, entitled IDENTITY AUTHENTICATION DEVICE AND FINGERPRINT SENSOR, issued to Miyakasa on Nov. 16, 2010, in which a fingerprint sensor array and local signal processing circuitry is contained in a separate housing separable from a user device and replaceable as a unit; and U.S. Pat. No. 7,755,369 B2, entitled CAPACITIVE FINGERPRINT SENSOR AND THE PANEL THEREOF, issued to Chuang et al. on Jul. 13, 2010 in which all of the sensor circuitry, including the controller IC and in-pixel high performance circuitry, such as amplification is formed in or on the glass substrate of a display unit. Such TFT-on-glass fingerprint readers almost always include pixel select and amplification circuitry at each array sensor pixel.
Two-dimensional capacitive fingerprint sensors can be more susceptible to noise and the effects of parasitic capacitances due to their larger size and array structure as compared, e.g., to a one-dimensional (linear array) sensor. For this reason virtually all current two-dimensional fingerprint sensors incorporate in-pixel amplification, and perhaps other signal processing, circuitry. However, this means the sensor array must be made on a silicon wafer or with a technology (such as higher quality TFT technology, that can use, e.g., such high quality and thus more expensive transistor fabrication technology, e.g., TFT fabrication technology, to provide high quality semiconductor devices such as may be required for such transistors in each pixel. This increases the cost of the sensor substantially compared to a flex or glass based passive sensor matrix, e.g., where the electrodes (traces) forming the sensor elements are printed or etched on a substrate generally in a single layer process, more like printed circuit board (“PCB”) fabrication process.